Comment 4 for bug 1048842

Joe, right now you can oversubscribe disk by creating a sparse image on whatever kind of virt layer you use. On XenServer at least, they call this thin provisioning. You can create a 100GB disk but the space is not pre-allocate until it is actually needed...

So there is no parameter exposing a disk oversubscription ratio in Nova because it's assuming for the moment that you handle this by configuring your disk appropriately at the hypervisor layer if you want oversubscription. The resource tracker only looks at the actual disk usage right now, so it interacts fine with this.

Also for CPUs, there is currently not any real resource tracking being done.

My preference is to not introduce new code for either disk or cpu oversubscription at this stage of Folsom and risk breakage, but I am looking at refactoring some of this for Grizzly.